If it did whole-program optimization, it theoretically could. But it is probably too costly. You don't have that much time and resources to optimize JIT, as you

If it did whole-program optimization, it theoretically could. But it is probably too costly. You don't have that much time and resources to optimize JIT, as you have doing static compilation. That's why, contrary to common beliefs on static vs dynamic compilation, still static compilers win in most cases, compared to even very mature things like JVM or .NET CLR, even though they have much easier task than JS.